You are exactly right! We were using TX/RX antenna port in the WBX receiver daughterboard. I get almost -170 dBm/Hz noise spectral density when I select RX2. This is almost perfect!
Thanks! Your email increased my pathloss calculation range by 30 dB :) Nazmul On Wed, Jun 27, 2012 at 9:22 AM, Jason Roehm <jas...@3db-labs.com> wrote: > Do you have the correct antenna port selected? I believe that RX2 is the > default for the SBX. If you are injecting signal into the port that isn't > selected, then you'll see ~30-40 dB of isolation in the front-end antenna > switch. That seems to be in the neighborhood of the difference that you're > seeing. > > Jason > > > On 06/27/2012 01:51 AM, Nazmul Islam wrote: > > Hello, > > I am trying to measure channel path loss using two USRP N210. I need to > measure the noise floor so that I can find the threshold for pathloss > measurement. I am using the attached flowgraph to calibrate the receiver > signal strength. I tried two ways to calibrate the receiver power and both > show me approximately -135 dBm/Hz noise spectral density. > > 1. At first I don't transmit anything and measure the power of the > floating point numbers that is coming out of rx USRP block. Then I > transmit a PN sequence of -5 dBm power at 17 MS/s from an USRP. I connect > this USRP through a 60 dB attenuator to the receiver USRP. This input (-65 > dBm) seems to double the power of the floating point numbers. I infer that > the my USRP noise floor is equivalent to -65 dB at 17 MHz. > > 2. I also apply an external 1 MHz noise source of -75 dBm power to the > receiver USRP. This leads to an increase of 3 dB power in the receiver FFT > plot. This also suggests I have -75 dBm noise power at 1 MHz. > > Both these experiments suggest -135 dBm/Hz noise spectral density in my rx > USRP. However, this is very far from theoretical noise spectral density > (approximately -170 dBm/Hz). My Rx USRP N210 has a WBX daughterboard and my > Tx USRP has an SBX daughterboard. The ettus websites suggest only 6 dB > noise figure (http://code.ettus.com/redmine/ettus/documents/16). If my > USRP daughterboard is not faulty, I must be giving some wrong parameters. I > put the RX gain as 30 dB to get the full range of WBX daughterboards ( > http://files.ettus.com/uhd_docs/manual/html/dboards.html). Shall I > increase it more? > > Thanks for your help. > > Nazmul > > > -- > Muhammad Nazmul Islam > > Graduate Student > Electrical & Computer Engineering > Wireless Information & Networking Laboratory > Rutgers, USA. > > > > _______________________________________________ > USRP-users mailing > listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > _______________________________________________ > USRP-users mailing list > usrp-us...@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > -- Muhammad Nazmul Islam Graduate Student Electrical & Computer Engineering Wireless Information & Networking Laboratory Rutgers, USA.
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